Radio communication system, communition terminal device, base station device, and radio communication method

ABSTRACT

A radio communication system carrying out uplink scheduling so as to reduce interference at a base station apparatus even when there are communication terminal apparatuses in the process of soft handover. In this system, a separation section ( 110 ) of a communication terminal apparatus separates a result of demodulation of a received signal into received data and a transmit power control (TPC) command instructing an increase or decrease of transmit power, a base station selection section ( 120 ) selects a main base station apparatus having the best channel quality according to the TPC command and outputs base station selection information. Furthermore, a transmit power control section ( 130 ) of the communication terminal apparatus determines transmit power according to the TPC command and an extra transmit power calculation section ( 140 ) calculates extra transmit power by subtracting the determined transmit power from maximum transmittable transmit power and outputs extra transmit power information. Furthermore, a selection/multiplexing section ( 150 ) of the communication terminal apparatus multiplexes transmission data, base station selection information and extra transmit power information and a transmission section ( 160 ) transmits the multiplexed data to the base station apparatus.

TECHNICAL FIELD

The present invention relates to radio a communication system,communication terminal apparatus, base station apparatus and radiocommunication method.

BACKGROUND ART

In a radio communication system in recent years, scheduling of datatransmission on a downlink such as HSDPA (High Speed Downlink PacketAccess) is attracting attention on one hand and scheduling of datatransmission on an uplink is under study on the other.

During scheduling on an uplink, a base station apparatus sequentiallyassigns data transmission timings to communication terminal apparatuseswithin the own cell and the communication terminal apparatuses transmittheir signals at the respective assigned transmission timings.

More specifically, for example, the base station apparatus estimates thechannel quality of the downlink up to the respective communicationterminal apparatuses from transmit power when transmitting signals tothe respective communication terminal apparatuses within the own cell.Then, uplink scheduling is realized by assigning transmission timings onthe uplink to the communication terminal apparatuses in descending orderof channel quality (e.g., see Unexamined Japanese Patent Publication No.2002-290327).

However, the above described uplink scheduling has a problem that evenwhen there is a communication terminal apparatus in the process of softhandover within the own cell, the base station apparatus performs uplinkscheduling regardless and independently of the base station apparatus atthe handover destination of the communication terminal apparatus in theprocess of soft handover. That is, when a communication terminalapparatus has established communications with a plurality of basestation apparatuses to realize soft handover, if the communicationterminal apparatus sends a signal at a transmission timing assigned byone base station apparatus, the signal also arrives at other basestation apparatuses which are communicating with other communicationterminal apparatuses and causes interference with their communications.

This problem will be explained more specifically with reference to FIG.1.

In FIG. 1, communication terminal apparatuses (MS) #3 and MS#4 arecommunicating with a base station apparatus (BTS) #1 and MS#5 and MS#6are communicating with a BTS#2. Furthermore, the MS#1 and MS#2 aremoving from the cell of the BTS#1 to the cell of the BTS#2 (or from thecell of the BTS#2 to the cell of the BTS#1) and are in the process ofsoft handover which allows the MS#1 and MS#2 to communicate with both ofthe base station apparatuses BTS#1 and BTS#2.

Under such circumstances, for example, the BTS#1 performs uplinkscheduling and a transmission timing is assigned to the MS#1 which is inthe process of soft handover. At this time, the MS#1 sends a signal atthe assigned transmission timing and this signal reaches not only theBTS#1 but also the BTS#2.

On the other hand, the BTS#2 is also autonomously performing uplinkscheduling and if a transmission timing has been assigned, for example,to the MS#6 when the signal from the MS#1 arrives, the signals from theMS#1 and MS#6 arrive at the BTS#2 simultaneously and the signal from theMS#1 to which no transmission timing is assigned constitutes aninterference component in the received signal of the BTS#2.

DISCLOSURE OF INVENTION

In a radio communication system which carries out uplink scheduling, itis an object of the present invention to provide a radio communicationsystem, communication terminal apparatus, base station apparatus andradio communication method capable of reducing interference at the basestation apparatus even when there is a communication terminal apparatusin the process of soft handover.

A subject matter of the present invention is for a communicationterminal apparatus in the process of soft handover to select a basestation apparatus having the best channel condition from among aplurality of base station apparatuses as a main base station apparatusand carry out data transmission under a condition according to thechannel condition up to the main base station apparatus.

The radio communication system in accordance with one aspect of thepresent invention is a radio communication system comprising a pluralityof base station apparatuses that send a transmit power control commandinstructing an increase or decrease of transmit power and a plurality ofcommunication terminal apparatuses that control transmit power accordingto the transmit power control command, wherein the communicationterminal apparatus comprises a reception section that receives thetransmit power control command, a selection section that selects a mainbase station apparatus having the best channel condition up to/from theown apparatus based on a history of the received transmit power controlcommands, a transmission section that transmits a signal using an errorcoding scheme and modulation scheme notified from the selected main basestation apparatus, and the base station apparatus comprises anauthorization section that authorizes the communication terminalapparatus having the maximum reception quality out of the communicationterminal apparatuses which have selected the own apparatus as the mainbase station apparatus to transmit a signal, a determining section thatdetermines an error coding scheme and modulation scheme used by thetransmission authorized communication terminal apparatus authorized totransmit a signal and a transmission section that transmits thedetermined error coding scheme and modulation scheme to the transmissionauthorized communication terminal apparatus.

In the above described radio communication system, the communicationterminal apparatus preferably further comprises a calculation sectionthat calculates extra transmit power by subtracting the transmit powerdetermined according to the transmit power control command from maximumtransmittable transmit power and the base station apparatus furthercomprises an estimation section that estimates reception qualitycorresponding to the communication terminal apparatus using the extratransmit power.

In accordance with another aspect of the present invention, thecommunication terminal apparatus comprises a reception section thatreceives transmit power control commands sent from a plurality of basestation apparatuses, a selection section that selects a main basestation apparatus having the best channel condition up to/from the ownapparatus based on a history of the received transmit power controlcommands and a transmission section that transmits base stationselection information that notifies the selected main base stationapparatus.

In the above described communication terminal apparatus, the selectionsection preferably stores the transmit power control commands for apredetermined time and selects a base station apparatus having thelargest difference obtained by subtracting the number of transmit powercontrol commands instructing an increase from the number of transmitpower control commands instructing a decrease as the main base stationapparatus.

In the above described communication terminal apparatus, the selectionsection preferably stores the transmit power control commands for apredetermined time and selects a base station apparatus having thelargest proportion of the number of transmit power control commandsinstructing a decrease in the number of transmit power control commandsstored as the main base station apparatus.

The above described communication terminal apparatus preferably furthercomprises a control section that determines transmit power according tothe transmit power control command and a calculation section thatcalculates extra transmit power by subtracting the determined transmitpower from the maximum transmit power transmittable from the ownapparatus.

In accordance with a further aspect of the present invention, the basestation apparatus comprises a reception section that receives basestation selection information sent by a communication terminal apparatuswhich notifies a main base station apparatus having the best channelcondition up to/from the communication terminal apparatus, anauthorization section that authorizes the communication terminalapparatus having the maximum reception quality out of the communicationterminal apparatuses which have selected the own apparatus as the mainbase station apparatus to transmit a signal, a determining section thatdetermines an error coding scheme and modulation scheme used by thetransmission authorized communication terminal apparatus which has beenauthorized to transmit a signal and a transmission section thattransmits the determined error coding scheme and modulation scheme tothe transmission authorized communication terminal apparatus.

The above described base station apparatus preferably further comprisesan estimation section that estimates reception quality corresponding tothe transmission authorized communication terminal apparatus using extratransmit power obtained by subtracting actual transmit power from themaximum transmit power transmittable by the transmission authorizedcommunication terminal apparatus and the determining section determinesan error coding scheme and modulation scheme according to the estimatedreception quality.

In the above described base station apparatus, the determining sectionpreferably determines an error coding scheme and modulation schemeaccording to the estimated reception quality and handover informationindicating whether the transmission authorized communication terminalapparatus is in the process of soft handover or not.

In the above described base station apparatus, the determining sectionpreferably comprises a prediction section that predicts a variation ofinterference power using extra transmit power of a communicationterminal apparatus other than the transmission authorized communicationterminal apparatus and determines an error coding scheme and modulationscheme according to the estimated reception quality and the predictedvariation of interference power.

The radio communication method in accordance with a still further aspectof the present invention is a radio communication method used in acommunication terminal apparatus, comprising a step of receivingtransmit power control commands transmitted from a plurality of basestation apparatuses, a step of selecting a main base station apparatushaving the best channel condition up to/from the communication terminalapparatus based on the history of the received transmit power controlcommands and a step of transmitting base station selection informationnotifying the selected main base station apparatus.

The radio communication method in accordance with a still further aspectof the present invention is a radio communication method used in a basestation apparatus, comprising a step of receiving base station selectioninformation transmitted by a communication terminal apparatus whichnotifies a main base station apparatus having the best channel conditionup to/from the communication terminal apparatus, a step of authorizingthe communication terminal apparatus having the maximum receptionquality out of the communication terminal apparatuses which haveselected the base station apparatus as the main base station apparatusto transmit a signal, a step of determining an error coding scheme andmodulation scheme used by the transmission authorized communicationterminal apparatus which has been authorized to transmit a signal and astep of transmitting the determined error coding scheme and modulationscheme to the transmission authorized communication terminal apparatus.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example of a radio communication system includingcommunication terminal apparatuses in the process of soft handover;

FIG. 2 is a block diagram showing the configuration of a communicationterminal apparatus according to an embodiment of the present invention;

FIG. 3 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 1 of the present invention;

FIG. 4 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 2 of the present invention; and

FIG. 5 is a block diagram showing the configuration of a base stationapparatus according to Embodiment 3 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, embodiments of the present invention will be described in detailwith reference to the attached drawings.

Embodiment 1

FIG. 2 is a block diagram showing the configuration of a communicationterminal apparatus according to Embodiment 1 of the present invention.The communication terminal apparatus shown in the figure is providedwith a reception section 100, a separation section 110, a base stationselection section 120, a transmit power control section 130, an extratransmit power calculation section 140, a selection/multiplexing section150 and a transmission section 160. Suppose the communication terminalapparatus shown in FIG. 2 is in the process of soft handover andreceiving signals from a plurality of base station apparatuses.

The reception section 100 receives a signal through an antenna, carriesout predetermined radio reception processing (down-conversion, A/Dconversion, etc.) and then demodulates the signal.

The separation section 110 separates the demodulation result intoreceived data and a transmit power control command instructing anincrease or decrease of transmit power (hereinafter referred to as “TPCcommand”) and outputs the TPC command to the base station selectionsection 120 and transmit power control section 130. Furthermore, whenthe demodulation result includes MCS (Modulation Coding Scheme)information indicating an error coding scheme and modulation scheme andtransmission authorization information indicating that data transmissionof the own apparatus is authorized, the separation section 110 outputsthe MCS information and transmission authorization information to thetransmission section 160 and selection/multiplexing section 150respectively.

The base station selection section 120 selects a base station apparatushaving the best channel quality from among a plurality of base stationapparatuses which can be communication partners as a main base stationapparatus according to the TPC command and outputs base stationselection information to notify the selected main base stationapparatus. More specifically, the base station selection section 120stores TPC commands sent from the plurality of base station apparatusesby base station apparatus, the sender, and by type of increase ordecrease for a predetermined time and selects a base station apparatushaving the largest difference obtained by subtracting the number of TPCcommands instructing an increase from the number of TPC commandsinstructing a decrease as the main base station apparatus. Then, thebase station selection section 120 outputs base station selectioninformation including a base station ID corresponding to the selectedmain base station apparatus.

Here, when transmit power of the communication terminal apparatus shownin FIG. 2 is excessive, a TPC command instructing a decrease is receivedand on the contrary when transmit power of the communication terminalapparatus shown in FIG. 2 is insufficient, a TPC command instructing anincrease is received. Therefore, when the difference obtained bysubtracting the number of TPC commands instructing an increase from thenumber of TPC command instructing a decrease received from the basestation apparatus is large, this indicates a strong tendency that thetransmit power for this base station apparatus is excessive and thechannel quality up to/from this base station apparatus is believed to begood.

Here, the base station selection section 120 is assumed to select thebase station apparatus having the largest difference obtained bysubtracting the number of TPC commands instructing an increase from thenumber of TPC commands instructing a decrease as the main base stationapparatus, but it is also possible to select, for example, a basestation apparatus having the largest proportion of the number of TPCcommands instructing a decrease in the number of TPC commands stored fora predetermined time as the main base station apparatus.

The transmit power control section 130 determines transmit poweraccording to a TPC command. More specifically, when at least one of TPCcommands sent from the respective base station apparatuses instructs adecrease, the transmit power control section 130 determines powerobtained by decreasing the previously determined transmit power by apredetermined amount as the transmit power this time and determines, inother cases (that is, when TPC commands sent from all the base stationapparatuses instruct an increase), power obtained by increasing thepreviously determined transmit power by a predetermined amount as thetransmit power this time.

The extra transmit power calculation section 140 calculates extratransmit power by subtracting the transmit power determined by thetransmit power control section 130 from the maximum transmit powertransmittable by the communication terminal apparatus shown in FIG. 2and outputs this calculation result as extra transmit power information.Therefore, the extra transmit power calculation section 140 constitutesa “calculation section.”

The selection/multiplexing section 150 multiplexes transmission data,base station selection information and extra transmit power informationand outputs the multiplexing result to the transmission section 160.Furthermore, when the separation section 110 outputs transmissionauthorization information indicating that data transmission of the ownapparatus is authorized, the selection/multiplexing section 150 outputsthe transmission data to the transmission section 160.

The transmission section 160 carries out error coding and modulation onthe multiplexed data output from the selection/multiplexing section 150,then carries out predetermined radio transmission processing (D/Aconversion, up-conversion, etc.) and transmits the data through anantenna with the transmit power determined by the transmit power controlsection 130. Here, the transmission section 160 carries out error codingand modulation on the multiplexed data based on the error coding schemeand modulation scheme according to the MCS information output from theseparation section 110.

FIG. 3 is a block diagram showing the configuration of the base stationapparatus according to this embodiment. The base station apparatus shownin the figure is provided with a reception section 200, a separationsection 210, an SIR measuring section 220, a reception qualityestimation section 230, a TPC command generation section 240, acommunication terminal selection section 250, an MCS selection section260, a multiplexing section 270, and a transmission section 280. Supposethe communication terminal apparatus shown in FIG. 2 is in the processof soft handover, communicates with a plurality of base stationapparatuses and all the base station apparatuses have the sameconfiguration as that shown in FIG. 3. Furthermore, since there is aplurality of communication terminal apparatuses including those in theprocess of soft handover within the cells of the respective base stationapparatuses, suppose the base station apparatus shown in FIG. 3 receivessignals from a plurality of communication terminal apparatuses.

The reception section 200 receives a signal through an antenna, carriesout predetermined radio reception processing (down-conversion, A/Dconversion, etc.) and then demodulates the signal.

The separation section 210 separates the demodulation result intoreceived data, base station selection information and extra transmitpower information, outputs the base station selection information to thecommunication terminal selection section 250 and outputs the extratransmit power information to the reception quality estimation section230.

The SIR measuring section 220 measures an SIR(Signal to InterferenceRatio) using the received signal.

The reception quality estimation section 230 estimates reception qualitycorresponding to the communication terminal apparatus which has sent thesignal using the measured SIR and extra transmit power information. Morespecifically, the reception quality estimation section 230 adds extratransmit power to the measured SIR to thereby estimate the receptionquality. Furthermore, when there is a possibility of multi-pathinterference, the reception quality estimation section 230 estimatesreception quality with the multi-path interference component corrected.

The TPC command generation section 240 compares the measured SIR with atarget SIR and generates a TPC command according to the comparisonresult. More specifically, when the measured SIR is equal to or smallerthan the target SIR, the TPC command generation section 240 generates aTPC command instructing an increase of transmit power, and on thecontrary when the measured SIR falls exceeds the target SIR, the TPCcommand generation section 240 generates a TPC command instructing adecrease of transmit power.

The communication terminal selection section 250 selects a communicationterminal apparatus for which data transmission is to be authorized basedon base station selection information from each communication terminalapparatus output from the separation section 210 and reception qualitycorresponding to each communication terminal apparatus output from thereception quality estimation section 230 and outputs transmissionauthorization information on the selected communication terminalapparatus. More specifically, the communication terminal selectionsection 250 references the base station selection information sent fromeach communication terminal apparatus, extracts the selectedcommunication terminal apparatuses which have selected the own apparatusas the main base station apparatus and selects the one having themaximum reception quality from among the extracted communicationterminal apparatuses. Therefore, the communication terminal selectionsection 250 constitutes an “authorization section.”

The MCS selection section 260 selects an error coding scheme andmodulation scheme used when the communication terminal apparatusselected by the communication terminal selection section 250 transmitsdata and outputs the selection result as MCS information to themultiplexing section 270. At this time, the MCS selection section 260selects an error coding scheme and modulation scheme most suitable forthis communication terminal apparatus based on the reception qualitycorresponding to the communication terminal apparatus for which datatransmission is authorized by the communication terminal selectionsection 250. Therefore, the MCS selection section 260 constitutes a“determining section.”

The multiplexing section 270 multiplexes the transmission data, TPCcommand, transmission authorization information and MCS information andoutputs the multiplexing result to the transmission section 280.

The transmission section 280 carries out predetermined radiotransmission processing (D/A conversion, up-conversion, etc.) on themultiplexed data output from the multiplexing section 270 and transmitsthe multiplexed data through the antenna.

Next, the operation of the communication terminal apparatus and basestation apparatus in the above described configurations will beexplained.

First, a signal including a TPC command from the base station apparatusis received by the reception section 100 through the antenna of thecommunication terminal apparatus. The received signal is subjected topredetermined radio reception processing and demodulated. Then, theseparation section 110 separates the demodulation result into thereceived data and TPC command and the TPC command is output to the basestation selection section 120 and transmit power control section 130.Here, since the communication terminal apparatus is in the process ofsoft handover, TPC commands are being sent from a plurality of basestation apparatuses which can be the communication partners and the TPCcommands sent from all the base station apparatuses are output to thebase station selection section 120 and transmit power control section130.

Then, the base station selection section 120 selects a base stationapparatus having the best channel quality up to/from the own apparatusas the main base station apparatus according to the history of the TPCcommands from the respective base station apparatuses. That is, the basestation selection section 120 uses TPC commands stored for apredetermined time, calculates the difference obtained by subtractingthe number of TPC commands instructing an increase from the number ofTPC commands instructing a decrease or calculating the proportion of thenumber of TPC commands instructing a decrease in the number of TPCcommands stored, etc., and thereby selects a base station apparatusestimated to have the best channel quality up to/from the own apparatusas the main base station apparatus. This selection result is output tothe selection/multiplexing section 150 as base station selectioninformation such as the base station ID of the main base stationapparatus.

On the other hand, the transmit power control section 130 determinestransmit power for data transmission according to the TPC commandoutput. That is, when at least one of the TPC commands sent from all thebase station apparatuses that can be communication partners instructs adecrease, the transmit power control section 130 determines the powerobtained by decreasing the previously determined transmit power by apredetermined amount as the transmit power this time and when the TPCcommands sent from all the base station apparatuses instruct anincrease, the transmit power control section 130 determines the powerobtained by increasing the previously determined transmit power by apredetermined amount as the transmit power this time. The determinedtransmit power is output to the transmission section 160 and output tothe extra transmit power calculation section 140 as well.

Then, the extra transmit power 140 calculates extra transmit power bysubtracting transmit power determined by the transmit power controlsection 130 from the maximum transmit power transmittable by the ownapparatus and outputs the result as the extra transmit power informationto the selection/multiplexing section 150.

When the base station selection information and extra transmit powerinformation are output to the selection/multiplexing section 150, theinformation and transmission data are multiplexed by theselection/multiplexing section 150 and the multiplexed data obtained isoutput to the transmission section 160. Then, the transmission section160 carries out predetermined radio transmission processing on themultiplexed data and transmits the multiplexed data through the antennawith transmit power determined by the transmit power control section130.

The transmitted signal is received by all base station apparatuses whichcan be the communication partners of the communication terminalapparatus including the main base station apparatus. Furthermore, othercommunication terminal apparatuses carry out processing similar to theabove described operation, signals including base station selectioninformation and extra transmit power information are sent and receivedby all base station apparatuses which can be the communication partnersof the respective communication terminal apparatuses.

The received signal received by the reception section 200 through theantenna of the base station apparatus is subjected to predeterminedradio reception processing and demodulated. Then, the separation section210 separates the demodulation result into received data, base stationselection information and extra transmit power information, and the basestation selection information is output to the communication terminalselection section 250 and the extra transmit power information is outputto the reception quality estimation section 230. Here, the base stationapparatus outputs the base station selection information and extratransmit power information sent from all the communication terminalapparatuses within the own cell to the communication terminal selectionsection 250 and reception quality estimation section 230 respectively.

On the other hand, the SIR measuring section 220 measures an SIR usingthe received signal received by the reception section 200. This measuredSIR is output to the reception quality estimation section 230 and TPCcommand generation section 240. Then, the TPC command generation section240 compares the measured SIR with a target SIR and generates a TPCcommand according to the comparison result. More specifically, when themeasured SIR is equal to or lower than the target SIR, the TPC commandgeneration section 240 generates a TPC command instructing an increaseof transmit power, and on the contrary when the measured SIR is equal toor higher than the target SIR, the TPC command generation section 240generates a TPC command instructing a decrease of transmit power. ThisTPC command is output to the multiplexing section 270.

Furthermore, the reception quality estimation section 230 uses themeasured SIR and extra transmit power information to estimate receptionquality corresponding to each communication terminal apparatus. That is,extra transmit power is added to the measured SIR and when multi-pathinterference is expected to occur, the interference component iscorrected and the reception quality corresponding to each communicationterminal apparatus is thereby estimated. This estimation result isoutput to the communication terminal selection section 250.

Then, using the estimation result output from the reception qualityestimation section 230 and the base station selection information, thecommunication terminal selection section 250 selects a communicationterminal apparatus for which data transmission is to be authorized. Thatis, the communication terminal selection section 250 references the basestation selection information sent from each communication terminalapparatus, extracts the communication terminal apparatuses which haveselected the own apparatus as the main base station apparatus andselects the one having the maximum reception quality from among thesecommunication terminal apparatuses as the communication terminalapparatus for which data transmission is authorized. Then, transmissionauthorization information on the selected communication terminalapparatus is output to the MCS selection section 260 and multiplexingsection 270.

When the transmission authorization information is output to the MCSselection section 260, the MCS selection section 260 selects an errorcoding scheme and modulation scheme to be used when the communicationterminal apparatus authorized to transmit data sends data and theselection result is output to the multiplexing section 270 as MCSinformation. Here, the selection of the MCS by the MCS selection section260 is carried out by selecting the error coding scheme and modulationscheme most suitable for this communication terminal apparatus based onthe reception quality corresponding to the communication terminalapparatus for which data transmission is authorized.

Furthermore, the communication terminal apparatus for which datatransmission is authorized is the one having the maximum estimatedreception quality out of the communication terminal apparatuses whichhave selected the own apparatus as the main base station apparatushaving the best channel quality. Therefore, the MCS selected by the MCSselection section 260 is the combination corresponding to the fastesttransmission rate out of the combinations of error coding schemes andmodulation schemes which are considered currently available. Thecommunication terminal apparatus carries out data transmission usingthis MCS, and can thereby shorten the time required for datatransmission by the communication terminal apparatus and reduceinterference with other communications.

When the TPC command, transmission authorization information and MCSinformation are output to the multiplexing section 270, the informationand transmission data are multiplexed by the multiplexing section 270and the multiplexed data obtained is output to the transmission section280. The transmission section 280 carries out predetermined radiotransmission processing on the multiplexed data and sends themultiplexed data through the antenna.

The transmitted signal is received by all communication terminalapparatuses which can be communication partners including thecommunication terminal apparatus for which data transmission isauthorized.

The received signal received by the reception section 100 through theantenna of the communication terminal apparatus is subjected topredetermined radio reception processing and demodulated. Then, theseparation section 110 outputs the MCS information of the demodulationresult to the transmission section 160 and outputs the transmissionauthorization information to the selection/multiplexing section 150. Inthis way, the communication terminal apparatus for which datatransmission is authorized is authorized to transmit data of the ownapparatus, and therefore the selection/multiplexing section 150 outputstransmission data to the transmission section 160, where error codingand modulation are carried out based on the error coding scheme andmodulation scheme according to the MCS information and the signal istransmitted through the antenna.

The transmission here is realized in the combination corresponding tothe fastest transmission rate out of the combinations of error codingschemes and modulation schemes which are considered available asdescribed above, and therefore the time required to transmit the sameamount of data is shortest and it is possible to thereby reduce thenumber of interference signals arriving at base station apparatusesother than the main base station apparatus and reduce interference atthe base station apparatuses.

Thus, according to this embodiment, the communication terminal apparatusselects a main base station apparatus having the best channel qualityfrom among base station apparatuses which can be communication partnersusing a history of TPC commands and transmits the base station selectioninformation, the base station apparatus selects the one having themaximum reception quality out of the communication terminal apparatuseswhich have selected the own apparatus as the main base station apparatusas the communication terminal apparatus for which data transmission isauthorized and determines the error coding scheme and modulation schememost suitable for the communication terminal apparatus and thecommunication terminal apparatus transmits data using the error codingscheme and modulation scheme, and therefore it is possible to use thecombination corresponding to the fastest transmission rate out ofcombinations of available error coding schemes and modulation schemes,minimize the time necessary to transmit a signal from the communicationterminal apparatus which produces interference with the base stationapparatuses other than the main base station apparatus and reduceinterference at the base station apparatuses in a radio communicationsystem which carries out uplink scheduling even when there arecommunication terminal apparatuses in the process of soft handover.

This embodiment has been explained assuming that the base stationapparatus multiplexes MCS information and a TPC command and sends themultiplexed data, but the present invention is not limited to this andany configuration can be adopted if it at least notifies the MCS mostsuitable for the communication terminal apparatus which is determined tobe authorized to transmit data based on the base station selectioninformation and extra transmit power information transmitted from thecommunication terminal apparatus to the communication terminalapparatus.

Furthermore, this embodiment has been explained assuming that the extratransmit power calculation section 140 provided for the communicationterminal apparatus calculates extra transmit power by subtractingtransmit power determined according to a TPC command from maximumtransmit power and the extra transmit power information is transmittedto the base station apparatus through the selection/multiplexing section150 and transmission section 160, but the present invention is notlimited to this and the communication terminal apparatus can alsomultiplex base station selection information and transmission datawithout being provided with or operating the extra transmit powercalculation section 140 and transmit this multiplexed data to the basestation apparatus through the transmission section 160. Furthermore, byso doing, the reception quality estimation section 230 at the basestation apparatus is also not necessary or need not be operated. Thus,by so doing, the base station apparatus determines the reception qualityof the communication terminal apparatus using only an SIR of thereceived signal, but it is sufficiently possible to select acommunication terminal apparatus having a good channel condition withthe base station apparatus.

Embodiment 2

A feature of Embodiment 2 of the present invention is that a basestation apparatus detects that a communication terminal apparatus is inthe process of soft handover and if the communication terminal apparatusfor which data transmission is to be authorized is in the process ofsoft handover, the base station apparatus changes the error codingscheme and modulation scheme assigned to this communication terminalapparatus to slower ones than those corresponding to the fastestavailable transmission rate.

FIG. 4 is a block diagram showing the configuration of the base stationapparatus according to Embodiment 2 of the present invention. In thebase station apparatus shown in the figure, the same components as thoseof the base station apparatus shown in FIG. 3 are assigned the samereference numerals and explanations thereof will be omitted.Furthermore, the configuration of the communication terminal apparatusaccording to this embodiment is the same as the configuration of thecommunication terminal apparatus according to Embodiment 1 (FIG. 2) andexplanations thereof will be omitted.

The base station apparatus shown in FIG. 4 is provided with a receptionsection 200, a separation section 210, an SIR measuring section 220, areception quality estimation section 230, a TPC command generationsection 240, a communication terminal selection section 250, an MCSselection section 260 a, a multiplexing section 270 and a transmissionsection 280.

The MCS selection section 260 a detects whether a communication terminalapparatus selected by the communication terminal selection section 250is in the process of soft handover or not based on handover informationindicating whether each communication terminal apparatus within the owncell is in the process of soft handover or not, selects an error codingscheme and modulation scheme used by this communication terminalapparatus to transmit data and outputs the selection result as MCSinformation to the multiplexing section 270. At this time, when thiscommunication terminal apparatus is not in the process of soft handover,the MCS selection section 260 a selects a combination of an availableerror coding scheme and modulation scheme corresponding to the fastesttransmission rate based on the reception quality corresponding to thecommunication terminal apparatus for which data transmission isauthorized by the communication terminal selection section 250. On theother hand, when the communication terminal apparatus is in the processof soft handover, the MCS selection section 260 a selects a combinationcorresponding to a lower transmission rate than the above describedcombination.

This allows the base station apparatus to receive data transmitted froma communication terminal apparatus in the process of soft handover morereliably and can thereby improve the throughput of the entire radiocommunication system.

Next, the operations of the communication terminal apparatus and basestation apparatus in the above described configurations will beexplained.

First, as in the case of Embodiment 1, the communication terminalapparatus selects a base station apparatus based on a history of TPCcommands. That is, the communication terminal apparatus selects a basestation apparatus having the best channel quality up to/from the ownapparatus as the main base station apparatus and transmits the selectionresult as base station selection information together with extratransmit power information to the communication terminal apparatus.

Then, as in the case of Embodiment 1, the base station apparatusreceives a signal, the reception quality estimation section 230estimates reception quality corresponding to each communication terminalapparatus from the extra transmit power information, the communicationterminal selection section 250 selects a communication terminalapparatus for which data transmission is to be authorized based on thisreception quality and base station selection information and outputstransmission authorization information to the MCS selection section 260a and multiplexing section 270.

When the transmission authorization information is output to the MCSselection section 260 a, the MCS selection section 260 a selects anerror coding scheme and modulation scheme used by the communicationterminal apparatus for which data transmission is authorized to transmitdata and outputs the selection result as MCS information to themultiplexing section 270. Here, when the communication terminalapparatus for which data transmission is authorized is not in theprocess of soft handover, the selection of MCS by the MCS selectionsection 260 a is realized by selecting a combination of an availableerror coding scheme and modulation scheme corresponding to the fastesttransmission rate, and when this communication terminal apparatus is inthe process of soft handover, the selection of MCS is realized byselecting a combination corresponding to a lower transmission rate thanthat of the above described combination.

As in the case of Embodiment 1, transmission authorization informationand MCS information are sent to the communication terminal apparatus andthe communication terminal apparatus authorized to transmit dataperforms error coding and modulation on transmission data based on theerror coding scheme and modulation scheme according to the received MCSinformation and transmits the data through the antenna.

Thus, according to this embodiment, when a communication terminalapparatus is in the process of soft handover, the base station apparatuschanges a combination of an error coding scheme and modulation scheme tobe instructed to the communication terminal apparatus for which datatransmission is to be authorized to one corresponding to a lowertransmission rate, and therefore the main base station apparatus canreceive data transmitted from the communication terminal apparatus inthe process of soft handover more reliably and improve the throughput ofthe entire radio communication system.

According to this embodiment, when an SIR (or estimated receptionquality estimated by the reception quality estimation section 230)measured by the SIR measuring section 220 is lower, it is possible tomake data reception by the main base station apparatus more reliable bychanging the combination of error coding scheme and modulation schemeselected by the MCS selection section 260 a to one corresponding to alower transmission rate. This is attributable to the fact about a fadingvariation that the probability of changing from a low level to a highlevel or from a high level to a low level is high, whereas theprobability of keeping a low level or high level is low.

Embodiment 3

A feature of Embodiment 3 of the present invention is that base stationapparatuses other than a main base station apparatus predictinterference power through data transmission from a communicationterminal apparatus.

FIG. 5 is a block diagram showing a base station apparatus according toEmbodiment 3 of the present invention. In the base station apparatusshown in the figure, the same components as those of the base stationapparatus shown in FIG. 3 are assigned the same reference numerals andexplanations thereof will be omitted. Furthermore, the configuration ofthe communication terminal apparatus according to this embodiment is thesame as the configuration of the communication terminal apparatusaccording to Embodiment 1 (FIG. 2) and explanations thereof will beomitted.

The base station apparatus shown in FIG. 5 is provided with a receptionsection 200, a separation section 210, an SIR measuring section 220, areception quality estimation section 230, a TPC command generationsection 240, a communication terminal selection section 250, an MCSselection section 260 b, a multiplexing section 270, a transmissionsection 280 and an interference power estimation section 300.

The MCS selection section 260 b selects an error coding scheme andmodulation scheme used when a communication terminal apparatus selectedby the communication terminal selection section 250 transmits data andoutputs the selection result as MCS information to the multiplexingsection 270. At this time, the MCS selection section 260 b selects anerror coding scheme and modulation scheme most suitable for thiscommunication terminal apparatus based on the reception qualitycorresponding to the communication terminal apparatus for which datatransmission is authorized by the communication terminal selectionsection 250 and the result of interference power estimation by theinterference power estimation section 300.

The interference power estimation section 300 predicts an increase in anamount of interference by communication terminal apparatuses which haveselected a base station apparatus other than the own apparatus as themain base station apparatus based on base station selection informationand extra transmit power information from each communication terminalapparatus output from the separation section 210. More specifically, theinterference power estimation section 300 extracts a communicationterminal apparatus having the maximum extra transmit power for eachgroup of communication terminal apparatuses which have selected a basestation apparatus other than the own apparatus as the main base stationapparatus and estimates a value obtained by multiplying the extratransmit power of this communication terminal apparatus by a probabilitythat the communication terminal apparatus may be authorized to transmitdata and correcting the multiplication result with a spreading factorcorresponding to the communication terminal apparatus as interferencepower by this communication terminal apparatus. Therefore, theinterference power estimation section 300 constitutes a “predictionsection.”

Next, the operations of the communication terminal apparatus and basestation apparatus in the above described configurations will beexplained.

First, as in the case of Embodiment 1, the communication terminalapparatus selects a base station apparatus based on a history of TPCcommands. That is, a base station apparatus having the best channelquality up to/from the own apparatus is selected as a main base stationapparatus by the communication terminal apparatus and the selectionresult is transmitted as base station selection information togetherwith extra transmit power information to the communication terminalapparatus.

Then, as in the case of Embodiment 1, the base station apparatusreceives the signal, the reception quality estimation section 230estimates reception quality corresponding to each communication terminalapparatus from the extra transmit power information, the communicationterminal selection section 250 selects a communication terminalapparatus for which data transmission is to be authorized based on thisreception quality and base station selection information and outputs thetransmission authorization information to the MCS selection section 260b and multiplexing section 270.

On the other hand, the interference power estimation section 300estimates interference power by the communication terminal apparatuseswhich have selected a base station apparatus other than the ownapparatus as the main base station apparatus based on the base stationselection information and extra transmit power information. That is, acommunication terminal apparatus having the maximum extra transmit poweris extracted for each group of communication terminal apparatuses whichhave selected each base station apparatus other than the own apparatusas the main base station apparatus and interference power is estimatedby multiplying the extra transmit power of this communication terminalapparatus by the probability that the communication terminal apparatusmay be authorized to transmit data and correcting the multiplicationresult with a spreading factor corresponding to the communicationterminal apparatus. This estimation result is output to the MCSselection section 260 b.

When the transmission authorization information and estimation result ofinterference power are output to the MCS selection section 260 b; theMCS selection section 260 b selects an error coding scheme andmodulation scheme used when a communication terminal apparatus for whichdata transmission is authorized transmits data and outputs the selectionresult as MCS information to the multiplexing section 270. Here, theselection of MCS by the MCS selection section 260 b is realized not onlyby selecting an error coding scheme and modulation scheme most suitablefor the communication terminal apparatus for which data transmission isauthorized but also by taking into account a predicted increase ininterference power. Therefore, compared to Embodiment 1, the selectederror coding scheme and modulation scheme correspond to the actualcommunication condition.

As in the case of Embodiment 1, transmission authorization informationand MCS information are sent to the communication terminal apparatus,the transmission data is subjected to error coding and modulation by thecommunication terminal apparatus for which data transmission isauthorized based on an error coding scheme and modulation schemeaccording to the received MCS information and sent through the antenna.

Thus, this embodiment predicts interference power by the communicationterminal apparatuses which have selected a base station apparatus otherthan the own apparatus as the main base station apparatus based on theextra transmit power information and selects an error coding scheme andmodulation scheme used by the communication terminal apparatus for whichtransmission is authorized by the own apparatus taking into account theinterference power, and therefore it is possible to allow thecommunication terminal apparatus to select an error coding scheme andmodulation scheme corresponding to the communication condition when thecommunication terminal apparatus actually transmits data, minimize thetime necessary to transmit a signal from the communication terminalapparatus, reduce interference and realize more accurate communications.

As explained above, according to the present invention, it is possibleto reduce interference at the base station apparatus in a radiocommunication system which performs uplink scheduling even when thereare communication terminal apparatuses in the process of soft handover.

Furthermore, according to the present invention, the communicationterminal apparatus selects a main base station apparatus having the bestchannel condition, the base station apparatus authorizes a communicationterminal apparatus having the maximum reception quality out of thecommunication terminal apparatuses which have selected the own apparatusas the main base station apparatus to transmit a signal and instructs anerror coding scheme and modulation scheme, and therefore thecommunication terminal apparatus can send the signal using a combinationcorresponding to the fastest transmission rate out of the combinationsof available error coding schemes and modulation schemes, and it ispossible to minimize a signal transmission time from the communicationterminal apparatus even when there are communication terminalapparatuses in the process of soft handover in a radio communicationsystem carrying out uplink scheduling and reduce interference at thebase station apparatus.

Furthermore, according to the present invention, the communicationterminal apparatus calculates extra transmit power and the base stationapparatus estimates reception quality using the extra transmit power,and therefore it is possible to estimate the reception qualitycorresponding to the communication terminal apparatus accurately anddetermine an error coding scheme and modulation scheme more suitable forthe transmission authorized communication terminal apparatus as a resultof using this estimation result to determine the error coding scheme andmodulation scheme used by the transmission authorized communicationterminal apparatus.

Furthermore, according to the present invention, a main base stationapparatus having the best channel condition up to/from the own apparatus(communication terminal apparatus) is selected based on the history oftransmit power control commands and the selection result is transmittedas base station selection information, and therefore the base stationapparatus can authorize a communication terminal apparatus having thebest channel condition to transmit data based on the base stationselection information and instruct the communication terminal apparatuson the optimal error coding scheme and modulation scheme, minimize thesignal transmission time from the communication terminal apparatusconsequently and reduce interference at the base station apparatus.

Furthermore, according to the present invention, the communicationterminal apparatus stores a transmit power control commands for apredetermined time and selects a base station apparatus having thelargest difference obtained by subtracting the number of transmit powercontrol commands instructing an increase from the number of transmitpower control commands instructing a decrease as the main base stationapparatus, and can thereby accurately select a base station apparatushaving the best channel condition as the main base station apparatus.

Furthermore, according to the present invention, the communicationterminal apparatus stores transmit power control commands for apredetermined time, selects a base station apparatus having the largestproportion of the number of transmit power control commands instructinga decrease in the number of transmit power control commands stored asthe main base station apparatus, and can thereby accurately select abase station apparatus having the best channel condition as the mainbase station apparatus.

Furthermore, according to the present invention, extra transmit power iscalculated by subtracting transmit power determined according to atransmit power control command from the maximum transmit powertransmittable by the communication terminal apparatus, and therefore thebase station apparatus can estimate reception quality using the extratransmit power and accurately estimate the reception qualitycorresponding to the communication terminal apparatus.

Furthermore, according to the present invention, a communicationterminal apparatus having the maximum reception quality out ofcommunication terminal apparatuses which have selected the own apparatusas the main base station apparatus is authorized to transmit a signaland instructed on an error coding scheme and modulation scheme, andtherefore the communication terminal apparatus can transmit a signalusing the combination corresponding to the fastest transmission rate outof the combinations of available error coding schemes and modulationschemes, minimize the signal transmission time from the communicationterminal apparatus even when there are communication terminalapparatuses in the process of soft handover in a radio communicationsystem which performs uplink scheduling and reduce interference at thebase station apparatus.

Furthermore, the present invention estimates reception qualitycorresponding to the transmission authorized communication terminalapparatus using extra transmit power, determines an error coding schemeand modulation scheme according to the estimation result, and canthereby determine an error coding scheme and modulation scheme moresuitable for the transmission authorized communication terminalapparatus.

Furthermore, according to the present invention, the base stationapparatus determines an error coding scheme and modulation schemeaccording to estimated reception quality and handover informationindicating whether the transmission authorized communication terminalapparatus is in the process of soft handover or not, and can therebyallow, for example, a communication terminal apparatus in the process ofsoft handover to use an error coding scheme and modulation schemecorresponding to a low transmission rate, perform reliablecommunications and improve the throughput of the entire radiocommunication system.

Furthermore, according to the present invention, the base stationapparatus predicts a variation in interference power using extratransmit power of a communication terminal apparatus other than atransmission authorized communication terminal apparatus and determinesan error coding scheme and modulation scheme according to the estimatedreception quality and predicted variation in interference power, andtherefore it is possible to select an error coding scheme and modulationscheme corresponding to the communication state when the communicationterminal apparatus actually transmits data, minimize the time necessaryto transmit a signal from the communication terminal apparatus, reduceinterference and carry out more accurate communications.

The present application is based on Japanese Patent Application No.2002-377433 filed on Dec. 26, 2002, entire content of which is expresslyincorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in a communication terminalapparatus, base station apparatus and radio communication system in amobile communication system which performs transmit power control.

1. A radio communication system comprising: a plurality of base stationapparatuses that send a transmit power control command instructing anincrease or decrease of transmit power; and a plurality of communicationterminal apparatuses that control transmit power according to saidtransmit power control command, wherein said communication terminalapparatus comprises: a reception section that receives said transmitpower control command; a selection section that selects a main basestation apparatus having the best channel condition up to/from the ownapparatus based on a history of said received transmit power controlcommands; and a transmission section that transmits a signal using anerror coding scheme and modulation scheme notified from the selectedmain base station apparatus, and said base station apparatus comprises:an authorization section that authorizes the communication terminalapparatus having the maximum reception quality out of the communicationterminal apparatuses which have selected the own apparatus as the mainbase station apparatus to transmit a signal; a determining section thatdetermines an error coding scheme and modulation scheme used by thetransmission authorized communication terminal apparatus authorized totransmit a signal; and a transmission section that transmits thedetermined error coding scheme and modulation scheme to saidtransmission authorized communication terminal apparatus.
 2. The radiocommunication system according to claim 1, wherein said communicationterminal apparatus further comprises a calculation section thatcalculates extra transmit power by subtracting the transmit powerdetermined according to said transmit power control command from maximumtransmittable transmit power, and said base station apparatus furthercomprises an estimation section that estimates reception qualitycorresponding to said communication terminal apparatus using said extratransmit power.
 3. A communication terminal apparatus comprising: areception section that receives transmit power control commands sentfrom a plurality of base station apparatuses; a selection section thatselects a main base station apparatus having the best channel conditionup to/from the own apparatus based on a history of said receivedtransmit power control commands; and a transmission section thattransmits base station selection information that notifies the selectedmain base station apparatus.
 4. The communication terminal apparatusaccording to claim 3, wherein said selection section stores saidtransmit power control commands for a predetermined time and selects abase station apparatus having the largest difference obtained bysubtracting the number of transmit power control commands instructing anincrease from the number of transmit power control commands instructinga decrease as the main base station apparatus.
 5. The communicationterminal apparatus according to claim 3, wherein said selection sectionstores said transmit power control commands for a predetermined time andselects a base station apparatus having the largest proportion of thenumber of transmit power control commands instructing a decrease in thenumber of transmit power control commands stored as the main basestation apparatus.
 6. The communication terminal apparatus according toclaim 3, further comprising: a control section that determines transmitpower according to said transmit power control command; and acalculation section that calculates extra transmit power by subtractingthe determined transmit power from the maximum transmit powertransmittable from the own apparatus.
 7. A base station apparatuscomprising: a reception section that receives base station selectioninformation sent by a communication terminal apparatus which notifies amain base station apparatus having the best channel condition up to/fromsaid communication terminal apparatus; an authorization section thatauthorizes the communication terminal apparatus having the maximumreception quality out of the communication terminal apparatuses whichhave selected the own apparatus as the main base station apparatus totransmit a signal; a determining section that determines an error codingscheme and modulation scheme used by the transmission authorizedcommunication terminal apparatus which has been authorized to transmit asignal; and a transmission section that transmits the determined errorcoding scheme and modulation scheme to said transmission authorizedcommunication terminal apparatus.
 8. The base station apparatusaccording to claim 7, further comprising an estimation section thatestimates reception quality corresponding to said transmissionauthorized communication terminal apparatus using extra transmit powerobtained by subtracting actual transmit power from the maximum transmitpower transmittable by said transmission authorized communicationterminal apparatus, wherein said determining section determines an errorcoding scheme and modulation scheme according to the estimated receptionquality.
 9. The base station apparatus according to claim 8, whereinsaid determining section determines an error coding scheme andmodulation scheme according to the estimated reception quality andhandover information indicating whether said transmission authorizedcommunication terminal apparatus is in the process of soft handover ornot.
 10. The base station apparatus according to claim 8, wherein saiddetermining section comprises a prediction section that predicts avariation of interference power using extra transmit power of saidcommunication terminal apparatus other than said transmission authorizedcommunication terminal apparatus, and determines an error coding schemeand modulation scheme according to the estimated reception quality andthe predicted variation of interference power.
 11. A radio communicationmethod used in a communication terminal apparatus, comprising: a step ofreceiving transmit power control commands transmitted from a pluralityof base station apparatuses; a step of selecting a main base stationapparatus having the best channel condition up to/from saidcommunication terminal apparatus based on the history of said receivedtransmit power control commands; and a step of transmitting base stationselection information notifying the selected main base stationapparatus.
 12. A radio communication method used in a base stationapparatus, comprising: a step of receiving base station selectioninformation transmitted by a communication terminal apparatus whichnotifies a main base station apparatus having the best channel conditionup to/from said communication terminal apparatus; a step of authorizingthe communication terminal apparatus having the maximum receptionquality out of the communication terminal apparatuses which haveselected said base station apparatus as the main base station apparatusto transmit a signal; a step of determining an error coding scheme andmodulation scheme used by the transmission authorized communicationterminal apparatus which has been authorized to transmit a signal; and astep of transmitting the determined error coding scheme and modulationscheme to said transmission authorized communication terminal apparatus.